Most sizing tools give you a single number and stop there. We wanted something closer to a reference book: a calculator that also shows you the whole chart it pulled that number from, plus a scale for how cup letters relate to actual volume as they climb.
Band and cup sizing is really just a small grid — a handful of bands across the top, a handful of bust-to-band differences down the side. Once you've seen the whole grid, sister sizes, brand quirks and the limits of a single letter all make a lot more sense. That's the gap this site tries to fill.
It is not a substitute for an in-person fitting, a medical device, or a diagnostic tool. It gives a mathematically sound reference from the two measurements you provide. Please read our disclaimer for the full picture.
BreastSizeCalculator.com is part of the Calculations.one family of single-purpose calculators. We keep each site small, fast, and free of unnecessary sign-ups.
Spotted an error in our chart or copy? Visit our contact page — we read every message ourselves.